Carrier units of this type are known from JP 62027626 A and weighing cells of this type are known from DE 33 30 988 C2.
In the present context, a weight switching unit is understood to mean, in general, a device for loading and unloading a load receiver of a weighing cell as required. In particular, substitution switching and adjustment switching are known. In the latter, a distinction is often made between calibration switching and linearization switching processes. Of particular interest are automated weight switching processes, such as are used particularly in electronic weighing cells in which the load receiver, for example, a boom arm, represents the connection between a weighing pan which supports the weight to be measured and an electronic weighing sensor.
Substitution switching processes usually serve to extend the measuring range. Electric weighing sensors, in particular those which operate using the principle of electromagnetic force compensation are mostly only available in a small but very accurately digitizable measuring current range. Since the measuring current or compensation current is in direct relation to the weight force loading the weighing sensor, this leads to a correspondingly small weight measuring range. In order to be able also to measure weights below the weight measuring range thus defined, it is known to “shift” the range into the permissible weight measuring range by additional loading of the weighing sensor with known substitution weights.
When adjustment switching is performed, by contrast, known adjusting weights are measured alone in order to determine and/or set instrument parameters. Calibration is normally said to occur when device parameters are determined under full load, whilst linearization is often considered to be when, to determine a, particularly, linear characteristic, device parameters are determined at multiple load levels and then interpolated or extrapolated for further load levels.
From the aforementioned DE 33 30 988 C2, there is known an electronic weighing cell of which the load receiver connects a weighing pan with a weighing sensor operating using the electromagnetic force compensation principle. Arranged below the weighing pan at the load receiver is a shift weight receiver for receiving shift weights as required. The shift weights are part of a weight switching device which is not in direct contact with the load receiver and consists of a carrier unit and an associated lifting unit. The shift weights mounted, with vertical play, in the carrier unit can be placed onto or lifted off the shift weight receiver individually or together by a vertical movement brought about by the lifting unit in order thereby to generate different substitution or adjustment states. Associated disadvantages are, in the case of substitution, the asymmetrical loading of the load receiver which can lead to tilting and thus to measuring errors (off-center load errors) and, in the case of adjustment, the small number of different, settable adjusting states.
From JP 62027626 A mentioned in the introduction, there is known a carrier unit of a weight switching device wherein a fork-shaped shift weight carrier is pivotably mounted on a motor-driven pivot shaft at the side facing away from the free ends of the carrier arms. A ring-shaped calibration weight lies on the free ends of the carrier arms so that a center of the ring corresponds with the center of the weighing pan post of a weighing cell. By pivoting the carrier unit, the ring-shaped calibration weight can be placed onto and lifted off the load receiver carrying the weighing pan post, concentrically with said post. In principle, the ring-shaped calibration weight would also be suitable as a substitution weight. However, a disadvantage is the low number of substitution or adjustment states that can be realized.
From DE 87 15 016 U1, there is known a weighing cell in which the adjusting weights lie, in the normal position, on a shift weight storage place arranged under the weighing pan and, when needed, are lifted out by two wedges which are displaceable by horizontally pivotable levers in the intermediate space between the device bottom and the shift weights and are pressed against an upper stop. Disadvantages herein again are the small number of adjustment and substitution states that can be created and the asymmetries thereof.
From DE 28 41 996 C2, there is known a weighing cell with a plurality of substitution weights symmetrically arranged in pairs. The substitution weights hang on cams of a plurality of cam shafts arranged over one another and can be lowered and raised in pairs together or individually onto/from shift weight receivers arranged over one another. Disadvantageous herein is the significant structural space required by the weight switching device.
Finally, from DE 10 2005 033 952 B4, there is known a monolithic weight switching device, the functional details of which are not, however, disclosed in said document.